That nursery plants don't yield much. I have, for a few years in a row, compared nursery tomatoes to seeds planted in my apartment and had far better yield from the seed plants. I got four or five tomatoes from the nursery plants. So I planted some seeds yesterday, I'm north of the 45th parallel at ~ 5,000ft.
I bought some seeds from an organic provider who is from my area and started a seed collection company. Seeds trust, they have seeds for every growing zone, lots of variety. So I bought a "can of seeds" from them several years ago and still have most of them. If stored properly seeds will remain viable for quite some time, organic seeds that is. I have a cache of seeds that I maintain so that I will always have a main ingredient for a food source should I need one. The tomatoes are called "Siberian tomatoes" and by gum, those plants give off roughly 20+ tomatoes each! And they taste great. One of my summer joys is a tomato sandwich with garden fresh tomato.
Anyway, It's not you so much as the quality of the plants you buy at the nursery, not what you think you're getting these days.